This project is designed to develop experimental and theoretical approaches to assess the radiotoxicity of low energy (including Auger) electrons, positron and alpha particles (especially astatine-211) to mammalian cells both in vitro and in vivo. We also plan to investigate the biological toxicity of the Auger effect using synchrotron radiation. The knowledge gained from these studies is helping in the development of a concrete strategy towards the use of unsealed radionuclides in the treatment and diagnosis of neoplastic disease. Furthermore, these studies have been extremely informative in determining the radiation dose delivered to various tissues by radiopharmaceuticals currently used in nuclear medicine. Finally, we intend to study the efficacy of using 77bromodeoxyuridine and astatinated targeted carriers in the treatment of tumor model.